In modern medical technology, implants are used on a continuously increasing degree. The implants are used for supporting vessels, hollow viscera, and vascular systems (endovascular implants), for attaching and temporarily fixing tissue implants and tissue transplants, or even for orthopedic purposes, e.g., as nails, plates, or screws. Frequently, only a temporary support or holding function until completion of the healing process or stabilization of the tissue is required and/or desired. In order to avoid complications which result from the implants remaining permanently in the body, the implants must either be operatively removed again or they are made of a material which is gradually degraded in the body, i.e., biodegradable. The number of biodegradable materials based on polymers or alloys is continuously growing, but in many areas of application, the mechanical properties of a metallic material are still indispensable. In practice, until now only a few metallic materials have proven themselves as biodegradable. At least metal alloys made of magnesium, iron, and tungsten have been suggested.
Inter alia, biodegradable magnesium alloys which are suitable for endovascular and orthopedic implants are known from EP 1 270 023. The alloys may contain up to less than 5 weight-percent rare earths.
However, most biodegradable alloys and polymers for medical implants known from the related art have the disadvantage that they are not detectable or are only detectable to an unsatisfactory extent in current x-ray methods. However, x-ray diagnosis is an important instrument for postoperative monitoring of the healing progress or for checking minimally invasive interventions. Thus, for example, stents have been placed in the coronary arteries during acute myocardial infarction treatment for some years. According to current methods, a catheter which carries the stent in an unexpanded state is positioned in the area of the lesion of the coronary vessel wall. Subsequently, the stent expands either through self-expansive forces or through inflation of a balloon, in order to prevent obstruction of the vessel wall in the expanded state. The procedure of positioning and expanding the stent must be monitored continuously during the procedure through interventional cardiology.
The x-ray visibility of an implant manufactured from a metallic or polymer material is a function of the thickness of the material and, in addition, of the linear extinction coefficient of the material. Iron as a component of medical steels has a linear extinction coefficient of 15.2 KeV/cm, for example, which is typically already insufficient for a contrast-rich monitoring image with the filigree structures of stents. Furthermore, it is known that the linear extinction coefficient becomes greater with increasing atomic number in the periodic system. Thus, for example, gold has a linear extinction coefficient of 101 KeV/cm.
Providing implants with a coating, a strip, or a marker which is incorporated or molded on in another way to improve the x-ray visibility is therefore known. Essentially the following points must be observed for the selection of the marker material:                the marker metal is not to worsen the mechanical properties of implant, in particular by increasing the rigidity,        the marker must be biocompatible, and        the marker may not flake or crack off during the implantation, in particular during the expansion or placement of a stent.        
Known marker methods provide attaching metal strips made of gold or other noble metals in specific areas of the stent, for example. Metal strips of this type may loosen, shift, or even fall off, however. A non-degradable marker made of a noble metal causes the expectation of the formation of a local element with the usually non-noble metals of the main body of implant, through which the marker itself may be resolved very rapidly from the structure. However, when the marker is dissolved very rapidly, this may also occur before the complete endothelialization; the marker may then float away and result in an embolization. Furthermore, there is the danger of abrasion of the intima during positioning of the implant.
With metal coating methods, radiopaque marking areas may be applied to the implants through chemical or physical vacuum deposition (CVD or PVD). Alternatively, methods such as ion beam assisted deposition (IBAD) and microfusion are suitable, using which very homogeneous coatings in the micrometer range are producible on the implant surface.
The application of marker layers and the positioning of marker elements on the implants made of biodegradable alloys or polymers are anything but trivial and typically requires individual tailoring of the material properties of the marker element to the further materials used in the implant and also adaptations in the design of the implant. Known attempted achievements of the object may therefore not be transferred without further steps to new materials, in particular the promising biodegradable alloys and polymers. Furthermore, the marker element itself is to be at least largely biodegradable or is at least to be converted into physiologically harmless components. These are understood as components which have dimensions significantly smaller than the dimensions of the marker before implantation, but which are not degraded further and are intercalated in the body in unchanged form.